Exploring a new generation of bimetallic magnetic ionic liquids with ultra-low viscosity in microextraction that enable direct coupling with high-performance liquid-chromatography.

BACKGROUND: The incorporation of bimetallic magnetic ionic liquids (MILs) in microextraction methods is an emerging trend due to the improved magnetic susceptibility offered by these solvents, which relies on the presence of metallic components in both the cation and the anion. This feature favors easy magnetic separation of these solvents in analytical sample preparation strategies. However, reported liquid-phase microextraction methods based on bimetallic MILs still present an important drawback in that the MILs are highly viscous, making a dispersive solvent during the microextraction procedure necessary, while also requiring a tedious back-extraction step prior to the chromatographic analysis. RESULTS: We propose for the first time a new generation of ultra-low viscosity bimetallic MILs composed of two paramagnetic Mn(II) complexes characterized by their easy usage in dispersive liquid-liquid microextraction (DLLME). The approach does not require dispersive solvent and the MIL-DLLME setup was directly combined with high-performance liquid chromatography (HPLC) and fluorescence detection (FD), without any back-extraction step. The approach was evaluated for the determination of five monohydroxylated polycyclic aromatic hydrocarbons, as carcinogenic biomarkers, in human urine. Optimum conditions of the MIL-DLLME method included the use of a low MIL volume (75 µL), a short extraction time (5 min), and no need of any dispersive solvent neither NaCl. The method presented limits of detection down to 7.50 ng L-1, enrichment factors higher than 17, and provided inter-day relative standard deviation lower than 11%. Analysis of urine samples was successfully performed, with biomarker content found at levels between 0.24 and 7.8 ng mL-1. SIGNIFICANCE: This study represents the first liquid-phase microextraction method using the new generation of low-viscous bimetallic MILs. The proposed MIL-DLLME approach represents 2 important advances with respect to previous methods employing bimetallic MILs: 1) no dispersive solvent is required, and 2) direct injection of the MIL in the HPLC is possible after minor dilution (no back extraction steps are required). Therefore, the microextraction strategy is simple, rapid, and consumes very small amounts of energy.

Magnetic Ionic Liquids in Analytical Microextraction: A Tutorial Review.

Magnetic ionic liquids (MILs) are materials of special interest in analytical chemistry and, particularly, in analytical microextraction. These solvents possess several of the properties derived from their inherent nature of ionic liquids, combined with their magnetism, that permits their manipulation with an external magnetic field. This feature allows for performing typical steps of the microextraction procedure in a simpler manner with the aid of a strong magnet. Although there are several important reviews summarizing the most innovative advances in this field, there is a gap of information, as they do not provide useful details and tips related to the experimental set up of these procedures. This tutorial review fills this gap by providing a guide for the proper handling of MILs, their manipulation with magnets, and their proper hyphenation with the most used analytical techniques. Attention is paid to dispersive liquid-liquid microextraction, stir-bar dispersive liquid microextraction, aqueous biphasic systems, and single-drop microextraction, for being the analytical microextraction techniques mostly employed with MILs. This review also introduces a classification of the MILs employed in analytical microextraction in three classes (denoted as A, B, and C) as a function of the MIL nature (metal-containing anion, metal-containing cation, and radical-containing ion), and discuss about the prospect and future trends regarding new MIL families in microextraction together with new directions expected in these procedures.

Mimicking human ingestion of microplastics: Oral bioaccessibility tests of bisphenol A and phthalate esters under fed and fasted states.

Notwithstanding the fact that microplastic fragments were encountered in the human stool, little effort has been geared towards elucidating the impact of chemical additives upon the human health. In this work, standardized bioaccessibility tests under both fasting and fed conditions are herein applied to the investigation of human oral bioaccessibility of plastic additives and monomers (i.e. eight phthalate esters (PAEs) and bisphenol A (BPA)) in low-density polyethylene (LDPE) and polyvinyl chloride (PVC) microplastics. The generation of phthalate monoesters is evaluated in the time course of the bioaccessibility tests. Maximum gastric and gastrointestinal bioaccessibility fractions are obtained for dimethyl phthalate, diethyl phthalate and BPA, within the range of 55-83%, 40-68% and 37-67%, respectively, increasing to 56-92% and 41-70% for dimethyl phthalate and diethyl phthalate, respectively, whenever their hydrolysis products are considered. Bioaccessibility fractions of polar PAEs are dependent upon the physicochemical characteristics of the microplastics, with greater bioaccessibility for the rubbery polymer (LDPE). With the method herein proposed, oral bioaccessible pools of moderately to non-polar PAEs can be also accurately assessed for risk-assessment explorations, with values ranging from 1.8% to 32.2%, with again significantly larger desorption percentages for LDPE. Our results suggested that the highest gastric/gastrointestinal bioaccessibility of the eight PAEs and BPA is reached under fed-state gastrointestinal extraction conditions because of the larger amounts of surface-active biomolecules. Even including the bioaccessibility factor within human risk assessment/exposure studies to microplastics, concentrations of dimethyl phthalate, di-n-butyl phthalate and BPA exceeding 0.3% (w/w) may pose severe risks after oral uptake in contrast to the more hydrophobic congeners for which concentrations above 3% (w/w), except for diethylhexyl phthalate, would be tolerated.

Microscale extraction versus conventional approaches for handling gastrointestinal extracts in oral bioaccessibility assays of endocrine disrupting compounds from microplastic contaminated beach sand.

The unified bioaccessibility method (UBM) was harnessed to assess in vitro oral bioaccessibility pools of dialkyl phthalate congeners (with methyl, -ethyl, -butylbenzyl, -n-butyl, -2-ethylhexyl, and -n-octyl moieties) and bisphenol A at the 17 µg g-1 level in beach sand contaminated with polyethylene microplastics. A variety of sample preparation approaches prior to the analysis of the UBM gastrointestinal extracts, including traditional methods (protein precipitation, liquid-liquid extraction, and solid-phase extraction) and dispersive liquid-liquid microextraction (DLLME) were comprehensively evaluated for clean-up and analyte enrichment. DLLME was chosen among all tested approaches on account of the high extraction efficiency (73-95%, excluding bis(2-ethylhexyl)phthalate and di-n-octyl phthalate), high sample throughput (∼7 min per set of samples), and environmental friendliness as demonstrated by the analytical eco-scale score of 83, and the green analytical procedure index pictogram with green/yellow labeling. The release of the less hydrophobic plastic-laden compounds (dimethyl phthalate, diethyl phthalate and bisphenol A) from the contaminated sample into the body fluids was significant, with bioaccessibility values ranging from 30 to 70%, and from 43 to 74% in gastric and gastrointestinal fluids, respectively, and with relative standard deviation < 17% in all cases. The majority of the compounds were leached during gastric digestion, likely as the combined action of the low pH and the gastric enzymes. The risk exposure analysis revealed that accumulation/concentration in the body fluids is potentially relevant for dimethyl phthalate, diethyl phthalate and bisphenol A, with relative accumulation ratios ranging from 1.1 ± 0.1 to 2.6 ± 0.4. The average daily intake values for the suite of compounds, corrected with the bioaccessibility fraction, ranged from 60 to 430 ng kg of body weight-1·day-1, in all cases, far below the tolerable daily intakes, thus indicating the lack of children health risk by ingestion of microplastic-laden sand with elevated concentrations of plasticizers.

Evolution and current advances in sorbent-based microextraction configurations.

This review overviews the main developments achieved in analytical sample preparation regarding the use of solid sorbents as extractants in different sorbent-based miniaturized, micro-scale and microextraction methods. Two main groups are proposed for the classification of the current approaches, based on their operational mode: micro-solid-phase extraction (µ-SPE) and solid-phase microextraction (SPME), while describing their respective main sub-modes: static- and dispersive-µ-SPE, and SPME with fibers and in tube SPME. Furthermore, other important sorbent-based microscale approaches (e.g., stir bar sorptive extraction, stir cake sorptive extraction, stir bar sorptive-dispersive microextraction, and thin film microextraction, among others) are also considered.

Fluorescence quenching of the SYBR Green I-dsDNA complex by in situ generated magnetic ionic liquids.

Magnetic ionic liquids (MILs) with metal-containing cations are promising extraction solvents that provide fast and high efficiency extraction of DNA. Hydrophobic MILs can be generated in situ in a methodology called in situ dispersive liquid-liquid microextraction. To consolidate the sample preparation workflow, it is desirable to directly use the DNA-enriched MIL microdroplet in the subsequent analytical detection technique. Fluorescence-based techniques employed for DNA detection often utilize SYBR Green I, a DNA binding dye that exhibits optimal fluorescence when bound to double-stranded DNA. However, the MIL may hinder the fluorescence signal of the SYBR Green I-dsDNA complex due to quenching. In this study, MILs with metal-containing cations were selected and their fluorescence quenching effects evaluated using FÓ§rster Resonance Energy Transfer and quantified using Stern-Volmer models. The MILs were based on N-substituted imidazole ligands (with butyl- and benzyl- groups as substituents) coordinated to Ni2+ or Co2+ metal centers as cations, and paired with chloride anions. The effects of NiCl2 and CoCl2 salts and of the 1-butyl-3-methylimidazolium chloride ionic liquid on the fluorophore complex were also studied to understand the components of the MIL structure that are responsible for quenching. The metal within the MIL chemical structure was found to be the main component contributing to fluorescence quenching. FÓ§rster critical distances between 11.9 and 18.8 Å were obtained for the MILs, indicating that quenching is likely not due to non-radiative energy transfer but rather to spin-orbit coupling or excited-state electron transfer. The MILs were able to be directly used in qPCR and fluorescence emission measurements using a microplate reader for detection, demonstrating their applicability in fluorescence-based detection methods. Graphical abstract.

High-throughput microscale extraction using ionic liquids and derivatives: A review.

Ionic liquids and derivatives-mainly polymeric ionic liquids and magnetic ionic liquids-have been extensively used in microscale extraction over the past few years. Current trends in analytical sample preparation gear toward linking microextraction approaches with high-throughput sample processing to comply with green analytical chemistry requirements. A variety of high sample throughput strategies that are coupled to both ionic-liquid-based solid-phase microextraction and ionic liquid-based liquid-phase microextraction are herein reported. The review is focused on microscale extraction methods that use (i) custom-made and dedicated extraction devices, (ii) parallel extraction, (iii) magnetic-based separation, and (iv) miniaturized systems employing semi-automatic or fully automatic flow injection methods, related micro/millifluidic devices, and robotic equipment.

Vacuum-assisted sorbent extraction: An analytical methodology for the determination of ultraviolet filters in environmental samples.

Vacuum-assisted sorbent extraction (VASE) has been applied in combination with gas chromatography-mass spectrometry for the determination of UV filters in water samples. VASE is a variant of headspace extraction which was developed in conjunction with the sorbent pen (SP) technology. This technique combines the advantages of both stir-bar assisted extraction and headspace solid-phase microextraction. The SP traps allowed both reduced pressure in-vial extraction and direct thermal desorption via a unique gas chromatographic injection port. The main parameters that affect the performance of VASE, including both extraction and desorption conditions, were extensively optimized. Under optimum conditions, extraction required 10 mL of sample within 40 mL vials, pH 3.5, ~30 s of air-evacuation, 14 h incubation at 70 °C, stirring at 200 rpm, and a final water management step conducted at ~ -17 °C for 15 min. Optimal thermal desorption required preheating at 260 °C for 2 min followed by desorption at 300 °C for 2 min. The beneficial effect of reduced-pressure extraction was demonstrated by comparing the UV filter extraction time profiles collected using VASE to an analogous atmospheric pressure procedure, resulting in up to a 3-fold improvement under optimized conditions. The VASE methodology enabled simultaneous extractions using different SPs without compromising the method reproducibility, which increases the overall sample throughput. The method was characterized by low limits of detection, from 0.5 to 80 ng L-1, and adequate reproducibility, with inter-SP and inter-day relative standard deviation lower than 14%. Tap and lake water was successfully analyzed with the proposed methodology, resulting in relative recoveries of spiked samples ranging between 70.0 and 120%.

Extraction of DNA with magnetic ionic liquids using in situ dispersive liquid-liquid microextraction.

A new class of magnetic ionic liquids (MILs) with metal-containing cations was applied in in situ dispersive liquid-liquid microextraction (DLLME) for the extraction of long and short double-stranded DNA. For developing the method, MILs comprised of N-substituted imidazole ligands (with butyl-, benzyl-, or octyl-groups as substituents) coordinated to different metal centers (Ni2+, Mn2+, or Co2+) as cations, and chloride anions were investigated. These water-soluble MILs were reacted with the bis[(trifluoromethyl)sulfonyl]imide anion during the extraction to generate a water-immiscible MIL capable of preconcentrating DNA. The feasibility of combining the extraction methodology with anion-exchange high-performance liquid chromatography with diode array detection (HPLC-DAD) or fluorescence spectroscopy was studied. The method with the Ni2+- and Co2+-based MILs was easily combined with fluorescence spectroscopy and provided a faster and more sensitive method than HPLC-DAD for the determination of DNA. In addition, the method was compared to conventional DLLME using analogous water-immiscible MILs. The developed in situ MIL-DLLME method required only 3 min for DNA extraction and yielded 1.1-1.5 times higher extraction efficiency (EFs) than the conventional MIL-DLLME method. The in situ MIL-DLLME method was also compared to the trihexyl(tetradecyl)phosphonium tris(hexafluorocetylaceto)nickelate(II) MIL, which has been used in previous DNA extraction studies. EFs of 42-99% were obtained using the new generation of MILs, whereas EFs of only 20-38% were achieved with the phosphonium MIL. This new class of MILs is simple and inexpensive to prepare. In addition, the MILs present operational advantages such as easier manipulation in comparison to hydrophobic MILs, which can have high viscosities. These MILs are a promising new class of DNA extraction solvents that can be manipulated using an external magnetic field. Graphical abstract Magnetic ionic liquids with metal-containing cations are applied in in situ dispersive liquid-liquid microextraction for the extraction of long and short double-stranded DNA.

Zwitterionic polymeric ionic liquid-based sorbent coatings in solid phase microextraction for the determination of short chain free fatty acids.

Five different zwitterionic sorbent coatings based on polymeric ionic liquids (PILs) were developed by the on fiber UV co-polymerization of the zwitterionic monomers 1-vinyl-3-(alkylsulfonate)imidazolium or 1-vinyl-3-(alkylcarboxylate)imidazolium and different dicationic ionic liquid (IL) crosslinkers. The developed sorbent coatings were applied in headspace solid-phase microextraction in combination with gas chromatography-mass spectrometry for the determination of short chain free fatty acids in wine. The sorbent coatings were found to extract these analytes via a non-competitive extraction mechanism. The methodology was optimized for the two best zwitterionic PIL coatings and compared to the commercially-available carboxen/polydimethylsiloxane (CAR/PDMS) and polyacrylate (PA) fibers. The sorbent coating based on the 1-vinyl-3-(propanesulfonate)imidazolium IL (Fiber 1) was more sensitive than PA while providing similar limits of detection to CAR/PDMS for the determination of analytes in a diluted synthetic wine sample. At the same time, Fiber 1 required lower extraction times (only 20 min versus 60 min for CAR/PDMS and 40 min for PA), exhibited higher reproducibility (with relative standard deviation lower than 8.9% for a spiked level of 7 µM) and was more tolerant to ethanol present within the sample. The zwitterionic PILs were also applied for the analysis of red wine, and the results were in agreement with those obtained for CAR/PDMS. The analytes were detected and quantified in the concentration range from 0.18 ±â€¯0.03 mg L-1 to 4.8 ±â€¯0.9 mg L-1, depending on the analyte and fiber.

In situ generation of hydrophobic magnetic ionic liquids in stir bar dispersive liquid-liquid microextraction coupled with headspace gas chromatography.

For the first time, an in situ stir bar dispersive liquid-liquid microextraction approach has been developed and coupled with headspace gas chromatography-mass spectrometry for the determination of a group of organic pollutants. The method exploits a new generation of magnetic ionic liquids (MILs) that contain paramagnetic cations based on Ni2+ or Co2+ metal centers coordinated with either N-butylimidazole or N-octylimidazole ligands and chloride anions. The reactants are added to an aqueous solution containing a high field neodymium rod magnet, followed by the addition of the bis[(trifluoromethyl)sulfonyl]imide anion that promotes a metathesis reaction for the in situ generation of a hydrophobic MIL. Concurrently, a high stirring rate is maintained to exceed the magnetic field of the rod magnet and disperse the generated MIL in the sample solution. When stirring is stopped, the MIL coats the rod magnet due to its paramagnetic nature, facilitating the MIL transfer and subsequent desorption and analysis. Under optimum conditions, the method required a 2.5-18% (w/v) aqueous solution of sodium chloride, 10 mL of sample, 20 or 30 mg of MIL, the addition of a small volume of dispersive solvent, and stirring for 5-7.5 min, depending on the MIL. The method provided limits of detection (LODs) down to 10 µg L-1, adequate reproducibility (with relative standard deviation values lower than 10% for a spiked level of 80 µg L-1), and relative recoveries between 72.5% and 102%. Furthermore, the method was successfully applied in the analysis of tap and mineral water.

In situ formation of hydrophobic magnetic ionic liquids for dispersive liquid-liquid microextraction.

A new class of magnetic ionic liquid (MIL) containing paramagnetic cations has been applied for in situ dispersive liquid-liquid microextraction in the determination of both polar and non-polar pollutants, including ultraviolet filters, polycyclic aromatic hydrocarbons, alkylphenols, a plasticizer and a preservative in aqueous samples. The MILs were based on cations containing Ni(II) metal centers coordinated with four N-alkylimidazole ligands and chloride anions. The MILs were capable of undergoing in situ metathesis reaction with the bis[(trifluoromethyl)sulfonyl]imide ([NTf2-]) anion during the microextraction procedure, generating a water-immiscible extraction solvent containing the preconcentrated analytes. The MIL was then isolated by magnetic separation, followed by direct analysis using reversed-phase high performance liquid chromatography with diode array detection. Among all of the studied MILs, those containing the N-butylimidazole and N-benzylimidazole ligands ([Ni(C4IM)42+]2[Cl-] and [Ni(BeIM)42+]2[Cl-], respectively) exhibited the best extraction performance. The method under optimum conditions required 5 mL of sample at pH 3, 20 mg of [Ni(C4IM)42+]2[Cl-] or 30 mg of [Ni(BeIM)42+]2[Cl-], 300 µL of acetone or acetonitrile as dispersive solvent (depending on the MIL), a 1:2 M ratio of MIL to [NTf2-], and 3 min of vortex. The developed method achieved higher extraction efficiency compared to the conventional MIL-dispersive liquid-liquid microextraction mode, with extraction efficiencies of 46.8-88.6% and 65.4-97.0% for the [Ni(C4IM)42+]2[Cl-] and the [Ni(BeIM)42+]2[Cl-] MILs (at a spiked level of 81 µg L-1), respectively, limits of detection down to 5.2 µg L-1, and inter-day relative standard deviation lower than 16%.

Silver-based polymeric ionic liquid sorbent coatings for solid-phase microextraction: Materials for the selective extraction of unsaturated compounds.

A new generation of silver-based polymeric ionic liquid (PIL) sorbent coatings has been developed and applied in solid-phase microextraction (SPME). The new materials are based on ionic liquid monomers formed by cations containing the silver(I) ion coordinated with two 1-vinylimidazole ligands. Up to seven different silver-based PIL sorbent coatings were developed by polymerizing the silver-IL monomer in the presence of either silver bis[(trifluoromethyl)sulfonyl]imide, and/or a dicationic ionic liquid crosslinker. The obtained sorbent coatings were found to possess adequate thermal stability despite the presence of the silver(I) ions. Thermal desorption of the analytes at 175 °C was effectively used without any significant decrease in extraction efficiency. The developed sorbent coatings were used in two different applications: the determination of alkenes/alkynes via headspace SPME and the determination of unsaturated fatty acids using direct-immersion SPME. In the former approach, the silver-based PILs were particularly selective for the determination of unsaturated compounds with terminal double bonds such as 1,5-hexadiene, 2-methyl-1,5-hexadiene, and 1,8-nonadiene. A study of the extraction mechanism of the analytes to the sorbent coating revealed a competitive partitioning of the analytes. In the second approach, the most selective silver-based PILs were applied for the determination of oleic acid, linoleic acid, and linolenic acid. After proper optimization of the method, the coatings were found to be more or as sensitive as the commercial polydimethylsiloxane fiber. Limits of detection between 2.6 and 8.2 µg L-1 in ultrapure water and from 12 to 14 µg L-1 in tap water were obtained for the best silver-based PIL, with relative standard deviations lower than 13% in all cases at a spiked level of 160 µg L-1. Finally, the fiber was effectively applied for the analysis of rinse water from a dairy farm, with adequate detection of the analytes at concentrations between 52 and 179 µg L-1.

Rapid analysis of ultraviolet filters using dispersive liquid-liquid microextraction coupled to headspace gas chromatography and mass spectrometry.

An ionic-liquid-based in situ dispersive liquid-liquid microextraction method coupled to headspace gas chromatography and mass spectrometry was developed for the rapid analysis of ultraviolet filters. The chemical structures of five ionic liquids were specifically designed to incorporate various functional groups for the favorable extraction of the target analytes. Extraction parameters including ionic liquid mass, molar ratio of ionic liquid to metathesis reagent, vortex time, ionic strength, pH, and total sample volume were studied and optimized. The effect of the headspace temperature and volume during the headspace sampling step was also evaluated to increase the sensitivity of the method. The optimized procedure is fast as it only required ∼7-10 min per extraction and allowed for multiple extractions to be performed simultaneously. In addition, the method exhibited high precision, good linearity, and low limits of detection for six ultraviolet filters in aqueous samples. The developed method was applied to both pool and lake water samples attaining acceptable relative recovery values.

Expanding the use of polymeric ionic liquids in headspace solid-phase microextraction: Determination of ultraviolet filters in water samples.

Three crosslinked polymeric ionic liquid (PIL) sorbent coatings were used in headspace solid-phase microextraction for the determination of a group of ultraviolet filters. The developed crosslinked PIL-based materials include two polycations and a double confined PIL. The method, in combination with gas chromatography-mass spectrometry, is simple, solvent free, and does not require of any derivatization step. After proper optimization of the methodologies with each developed fiber, the analytical performance was compared with a commercial polyacrylate fiber. A study of the normalized calibration slopes, obtained by dividing the calibration slope of each analyte by the coating volume, revealed that the crosslinked fibers can be used as alternatives to commercial fibers for the determination of the selected group of compounds. In particular, the coating nature of the PIL containing the 1-vinylbenzyl-3-hexadecylimidazolium bis[(trifluoromethyl)sulfonyl]imide IL as monomer and the 1,12-di(3-vinylbenzylimidazolium)dodecane bis[(trifluoromethyl)sulfonyl]imide IL as crosslinker is the most suitable for the extraction of the selected compounds despite their coating volume, being 3.6 times lower than the commercial polyacrylate fiber. For this fiber, wide linear ranges, correlation coefficients higher than 0.990, limits of detection ranging from 2.8 ng L-1 to 26 ng L-1 and relative standard deviations ranging from 2.5 to 15% were achieved. Finally, all proposed PIL-based fibers were applied towards the analysis of tap water, pool water and lake water, with the majority of the ultraviolet filters being detected and quantified in the last two types of samples.

Advances in the analysis of biological samples using ionic liquids.

Ionic liquids are a class of solvents and materials that hold great promise in bioanalytical chemistry. Task-specific ionic liquids have recently been designed for the selective extraction, separation, and detection of proteins, peptides, nucleic acids, and other physiologically relevant analytes from complex biological samples. To facilitate rapid bioanalysis, ionic liquids have been integrated in miniaturized and automated procedures. Bioanalytical separations have also benefited from the modification of nonspecific magnetic materials with ionic liquids or the implementation of ionic liquids with inherent magnetic properties. Furthermore, the direct detection of the extracted molecules in the analytical instrument has been demonstrated with structurally tuned ionic liquids and magnetic ionic liquids, providing a significant advantage in the analysis of low-abundance analytes. This article gives an overview of these advances that involve the application of ionic liquids and derivatives in bioanalysis. Graphical abstract Ionic liquids, magnetic ionic liquids, and ionic liquid-based sorbents are increasing the speed, selectivity, and sensitivity in the analysis of biological samples.

Magnetic ionic liquids as extraction solvents in vacuum headspace single-drop microextraction.

A vacuum headspace single-drop microextraction method based on the use of magnetic ionic liquids (vacuum MIL-HS-SDME) for the determination of short chain free fatty acids is described for the first time. The basis of the method involves the use of a rod magnet to aid in maintaining a small microdroplet of magnetic ionic liquid (MIL) during headspace single-drop microextraction (HS-SDME). The application favors reduced pressure conditions inside the sampling vial while maintaining the MIL droplet in the headspace. After extraction, the MIL microdroplet containing extracted FFAs is transferred to a headspace vial where static headspace desorption is performed, followed by gas chromatographic-mass spectrometry (GC-MS) analysis. A number of MILs were studied and the trihexyl(tetradecyl)phosphonium tris(hexafluoroacetylaceto)manganate(II) MIL was found to be the most suitable for the proposed method. A comparison with atmospheric pressure MIL-HS-SDME revealed that analytes reached equilibrium faster when reduced pressure conditions were applied and that an enhancement in the extraction efficiency of analytes under these vacuum conditions was observed at any extraction time. Under optimum conditions, the method requires only 20µL of MIL placed at the end of a rod magnet and the evacuation of air using a modified extraction vial and a vacuum pump. Afterwards, 10mL of sample containing 30% (w/v) of NaCl is injected in the vial and the vacuum MIL-HS-SDME is performed at 45°C and 600rpm for 60min. The MIL microdroplet can easily be transferred to a 4.2mL modified headspace vial for the headspace desorption and GC-MS analysis. The entire method is characterized by wide linearity ranges, low limits of detection for analytes (down to 14.5µgL-1), good reproducibility (with relative standard deviation lower than 13%), and relative recoveries ranging from 79.5% to 111%. The proposed vacuum MIL-HS-SDME was applied towards the analysis of two different milk samples with the majority of analytes being detected and quantified.

Non-conventional solvents in liquid phase microextraction and aqueous biphasic systems.

The development of rapid, convenient, and high throughput sample preparation approaches such as liquid phase microextraction techniques have been continuously developed over the last decade. More recently, significant attention has been given to the replacement of conventional organic solvents used in liquid phase microextraction techniques in order to reduce toxic waste and to improve selectivity and/or extraction efficiency. With these objectives, non-conventional solvents have been explored in liquid phase microextraction and aqueous biphasic systems. The utilized non-conventional solvents include ionic liquids, magnetic ionic liquids, and deep eutectic solvents. They have been widely used as extraction solvents or additives in various liquid phase microextraction modes including dispersive liquid-liquid microextraction, single-drop microextraction, hollow fiber-liquid phase microextraction, as well as in aqueous biphasic systems. This review provides an overview into the use of non-conventional solvents in these microextraction techniques in the past 5 years (2012-2016). Analytical applications of the techniques are also discussed.

Vacuum-assisted headspace-solid phase microextraction for determining volatile free fatty acids and phenols. Investigations on the effect of pressure on competitive adsorption phenomena in a multicomponent system.

This work proposes a new vacuum headspace solid-phase microextraction (Vac-HSSPME) method combined to gas chromatography-flame ionization detection for the determination of free fatty acids (FFAs) and phenols. All target analytes of the multicomponent solution were volatiles but their low Henry's Law constants rendered them amenable to Vac-HSSPME. The ability of a new and easy to construct Vac-HSSPME sampler to maintain low-pressure conditions for extended sampling times was concurrently demonstrated. Vac-HSSPME and regular HSSPME methods were independently optimized and the results were compared at all times. The performances of four commercial SPME fibers and two polymeric ionic liquid (PIL)-based SPME fibers were evaluated and the best overall results were obtained with the adsorbent-type CAR/PDMS fiber. For the concentrations used here, competitive displacement became more intense for the smaller and more volatile analytes of the multi-component solution when lowering the sampling pressure. The extraction time profiles showed that Vac-HSSPME had a dramatic positive effect on extraction kinetics. The local maxima of adsorbed analytes recorded with Vac-HSSPME occurred faster, but were always lower than that with regular HSSPME due to the faster analyte-loading from the multicomponent solution. Increasing the sampling temperature during Vac-HSSPME reduced the extraction efficiency of smaller analytes due to the enhancement in water molecule collisions with the fiber. This effect was not recorded for the larger phenolic compounds. Based on the optimum values selected, Vac-HSSPME required a shorter extraction time and milder sampling conditions than regular HSSPME: 20 min and 35 °C for Vac-HSSPME versus 40 min and 45 °C for regular HSSPME. The performance of the optimized Vac-HSSPME and regular HSSPME procedures were assessed and Vac-HSSPME method proved to be more sensitive, with lower limits of detection (from 0.14 to 13 µg L-1), and better intra-day precision (relative standard deviations values < 10% at the lowest spiked level) than regular HSSPME for almost all target analytes. The proposed Vac-HSSPME method was successfully applied to quantify FFAs and phenols in milk and milk derivatives samples.